Studies On Early Fish Resources In Jiangjin Cross-section In The Upstream Of Yangtze River

Fish, especially the rare and endemic species, are abundant in the upper reaches of Yangtze River. However, the habitat of fish has been greatly induced by the increased water level in the Three Gorges Reservoir and a series of hydropower stations located on the lower reaches of Jinsha River, i.e., Xiangjiaba Power Station and Xiluodu Power Station, which take a great threat to the resources of Four Famous Chinese carps and Coreius heterodon. Therefore, surveys for early fish resources were carried out in the upper reaches of the Yangtze River from May to July in 2009. Four contents were researched in the survey, which included the species composition of egg and larval resources, the quantity of egg and larval resources, the temporal and spatial variation of egg and larval resources and the relations between the quantity of egg and larval resources and the main environment factors of Jiangjin cross section in the upper reaches of Yangtze River. All of them could provide the scientific bases for the protection of early fish resources in the upper reaches of Yangtze River.During the 59 days' survey,1782 fish eggs and 2721 fish larva were collected and the total sampling time were 5410 minutes. There were an estimated of 26.8×108 ind early fish resources, which included 10.9×108 fish eggs and 15.9×108 fish larva. Recognized fish species drifting through the sampling site were Salangichthys tangkahkeii, Botia superciliaris, Leptobotia elongate, Leptobotia rubrilaris, Lepturichthys fimbriata, Jinshaia sinensis, Parabotia bimaculata, Parabotia fasciata, Zacco platypus, Ctenopharyngodon idellus, Aristichthys nobilis, Hypophthalmichthys molitrix, et al. more than 30 fish species. In those fish, Culterinae took account of 21.03%, Cobitidae took account of 13%, Rhinogobius giurinus took account of 10.68%, four famous Chinese carps took account of 9.26%.In the survey, there were large numbers of egg and larval resources of four famous Chinese carps and Coreius heterodon from Yibin to Chongqing section in the upper reaches of Yangtze River. In four famous Chinese carps, Ctenopharyngodon idellus, Hypophthalmichthys molitrix and Aristichthys nobilis took the great part and there was no Mylopharyngodon piceus found, for which the ratio were 34.5%,64.4%and 1.1%. There were an estimated amount of 3.76×108ind of egg and larval resources of four famous Chinese carps and 2.52×108 ind of egg and larval resources of Coreius heterodon drifting through the Jiangjin cross section. According to the development stage observed, the main spawning sites of the four famous Chinese carps were distributed 54-140 km upstream from the Jiangjin cross section, that is between Zhuyang town and Mituo town. The spawning sites of Coreius heterodon were dispersive and there were three main spawning sites which are 10-47 km upstream between Longmen beach and Zhutuo town,58-111 km upstream between Zhuyang town and Hejiang county town,58-111 km upstream between Mituo town and Luzhou city.Day and night survey findings showed that in Jiangjin cross section, there was no obvious variation between day and light for drifting fish eggs, and the drifting larvae density was higher after sunrise (10:30) and before sundown (18:30), and lower in noon (12:30) and before sunrise (6:30). However, the results tested by Wilcoxon signed rank test showed that there was no significant difference in drifting larvae density (P=0.347). What's more, there was no distinct difference between morning sampling and afternoon sampling when water discharge was stable in Jiangjin cross section (P>0.05).The result of horizontal distribution sampling indicated that there was no significant difference in distribution density between north bank and south bank (P>0.05) for drifting fish eggs (P=0.782) and drifting larvae (P=0.073) However, there were both dramatic differences in horizontal distribution density between two banks and middle area (P＜0.01).The drifting fish eggs and larvae density showed that there was no significant difference in vertical distribution density for drifting eggs and larvae, the test coefficient for fish eggs was 0.784 and for fish larvae was 0.898 in north bank; and the test coefficient for fish eggs was 0.958 and for fish larvae was 0.095 in south bank. The result were caused by some reasons as follows, one was that the fish eggs and larvae collected in Jiangjin cross section were in the early development stage with poor swimming ability, and another was that the complex hydrologic environment in the upper of Yangtze river mixed them.The rate of flow between May to June was relatively low in 2009 in the upper of Yangtze River. As the rainy season was coming in the middle of June, the rate of flow was increasing, the range of water temperature in river was between 21.4 to 25.2℃, the range of transparency was between 5 to 37 cm, the range of dissolved oxygen was between 5.3 to 8.3 mg/L, the range of pH was 7.8 to 8.2. The water level, transparency and rate of flow had significant correlation (P<0.001), and the dissolved oxygen and temperature had significant correlation (P＜0.001) too.During the survey, the drifting fish eggs and larvae density of four famous Chinese carps had significant correlation with rate of flow, water level, transparency, temperature and dissolved oxygen which indicating that environment factors had a great influence for reproduction activity of four famous Chinese carps The spawning time of four famous Chinese carps were not coherent, the larvae density was highest at the beginning of June. During that period, the range of temperature was between 22.1 to 25.2℃, the range of dissolved oxygen was between 5.85 to 8.08 mg/L,.During the survey, the drifting fish eggs and larvae density of Coreius heterodon had no significant correlation with rate of flow, water level, transparency, temperature and dissolved oxygen.which indicating that environment factors had no great influence for reproduction activity of Coreius heterodon The spawning peak time of Coreius heterodon were dispersive. During that period, the range of temperature was between 21.6 to 25.2℃, the range of dissolved oxygen was between 5.85 to 8.04 mg/L,.